This application claims the priority of German Application 19940703.7, filed Aug. 27, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention concerns a process and a device for engine and transmission control.
In motor vehicles with internal combustion engines, the speed and torque range of the engine is reproduced in the speed and torque range of the wheels through a transmission.
In older vehicles, an accelerator is connected directly with the throttle of a vehicle, so that an engine torque corresponding to the application of the accelerator results. This torque is transferred to the drive wheels according to the gear ratio. If a stepped automatic transmission is used between the propulsion engine and the drive wheels, then in this embodiment a step-shaped trace of the transmission output torque resulting from gear shifting is produced.
However, mechanically decoupling the accelerator from the throttle is also known. In U.S. Pat. No. 4,893,526, for example, a desired value for a transmission output torque is determined from the longitudinal speed of the vehicle and the position of the accelerator pressed by the driver. Thus, the accelerator position does not directly indicate the engine output torque, but rather ends up determining an output torque on the wheels which is directly dependent on the desired transmission output torque.
According to U.S. Pat. No. 4,893,526, a desired engine speed is determined depending on this transmission output torque, which is set by the adjustment of a continually adjustable vehicle transmission. The motor and the transmission are thus operated by an engine control or a transmission control, respectively.
A control is known from the VDI [German Engineering Society] Magazine, special issue xe2x80x9cAbtriebstechnikxe2x80x9d [Drive Technology], issue 134, March 1992, pp. 26-49, which determines a desired engine speed dependent on the throttle angle, and also sets that speed by adjustment of a continually adjustable transmission.
A system for setting a gear ratio is described in German Patent DE 196 26 936 A1, in which first a desired speed of the engine is determined, and the gear ratio of the transmission is adjusted depending on this desired speed. At least one of the dimensions influencing or representing the driving situation and/or the driving conditions is then determined and the determination of the desired speed of the motor is performed according to this dimension.
A process and a device for control of the drivetrain of a vehicle is known from German Patent DE 197 03 863 A1. While driving, a desired value for the output torque of the vehicle or for the transmission output torque, respectively, is preset. The different operating points of the drivetrain are characterized by output torques of the propulsion unit and speed gear ratios which differ as little as possible. Assessment dimensions are then determined for possible operating points while driving. An optimal operating point is then selected, and the transmission is set correspondingly. As an alternative to setting the gear ratio, the output speed of the propulsion unit corresponding to the operating point selected can also be set by an alteration of the gear ratio.
All of the above-mentioned technical literature is similar in that an engine speed is set by adjustment of the transmission. It is thereby possible to realize continuous wheel torque traces (e.g. hyperbolic traces of equal propulsion performance). In stepped automatic transmissions, this type of adjustment is not possible without further measures due to the discrete gear ratio changes.
In any case, a type of adjustment is also sought for stepped automatic transmissions that, in addition to other designs, allows the wheel output torque (wheel torque) to be changed continuously at a constant accelerator position over the vehicle speed. This relationship is shown in FIG. 7. The black dashed lines indicate the relationship between the driving speed and the wheel torque at each fixed gear ratio (1st gear-5th gear) and maximum accelerator angle (engine full load). The solid black line shows the wheel torque trace when using a stepped automatic transmission with normal control at partial accelerator position (engine partial load). The white dashed line shows the physical maximum limit curve with decoupling of the throttle (engine full load) from the accelerator position (partial accelerator position). The hyperbolic gray solid line represents a wheel torque/vehicle speed trace for partial accelerator position as desired for reasons of drivability and driving performance (desired trace). Such a trace represents a continuous traction trace, for which essentially no discontinuities occur in the output torque trace if gear shifting is not considered.
The goal of the present invention is to reproduce this type of behavior with stepped automatic transmissions as well.
A further goal is to realize any desired wheel torque and/or transmission output torque which deviates from the hyperbolic shape without discontinuities. It is particularly noted that the wheel torque and the transmission output torque essentially correspondxe2x80x94apart from a multiplication factor.
The present invention provides drive management based on torque coordination. A torque of the drive wheels desired by the driver (wheel torque and/or transmission output torque) is realized, in that during, as well as outside of, a gear shift of the stepped automatic transmission, desired engine torques and consequently engine torque defaults, namely desired engine torque defaults affecting the filling and ignition, are calculated. These desired engine torques or engine torque defaults, respectively, are calculated by the totality of the torque coordinator, engine control, and transmission control and are converted within the bounds of physical limits. The actual transmission output torque is determined from the torque actually realized from the motor within the bounds of physical limits. Discontinuities are essentially avoided by the permanent realization of this transmission output torque, even during gear shifting.
When the stepped automatic transmission is not shifting gears, the desired torque is attained by calculating, depending on the gear ratio and the default transmission output torque, at least an engine torque default affecting the filling M_IND_ACC and/or an engine torque default affecting the ignition M_IND_GS. A definite engine torque should thereby be attained which, while shifting between the known gear ratios, provides exactly the default transmission output torque. The engine torque defaults M_IND_ACC and M_IND_GS are transmitted to the engine control and are realized by way of the control of the filling and ignition. In so doing, other parameters could possibly be included in the calculation and/or conversion of the engine torques in the controls (engine control and transmission control).
Within the physical limits of the engine, the torque defaults are generally fulfilled; the transmission output torque 10 is thus, except for shifting gears, adjusted. If the engine cannot achieve the torque default, a transmission output torque and/or wheel torque resulting from the realizable engine torque M_IND and the corresponding gear ratios is produced which deviates from the default.
During gear shifting of the stepped automatic transmission, the realization of the transmission output torque essentially occurs via a friction element provided in the stepped automatic transmission. A specific torque is transmitted corresponding to the control variable selected for the friction element. Therefore, the control variable is set during gear shifting so that exactly the desired transmission output torque is attained.
However, the load on the friction element during gear shifting from the friction output produced by slip can be problematic. To increase the service life of the friction element, it is therefore advisable to keep the friction output within a preset level. This type of adjustment has already been described in principle in German Patent DE 43 27 906 A1, in which either an ignition control and/or a control of filling to reduce the engine torque is described. With this type of influence, the engine can be adjusted to a default speed trace.
The engine torque defaults are therefore coordinated in such a fashion that first a synchronization engine torque M_IND_SYNC is calculated, which provides the engine torque required at the moment after shifting gears. The torque M_IND_ACC affecting the filling is calculated at least from the synchronization engine torque, and the engine torque M_IND_GS affecting the ignition is determined in such a way that a default speed trace dependent on the gear ratio change when shifting the transmission can be set. Except for the slip condition, the friction element of the transmission output torque and/or wheel torque is not influenced by the correction of the torque M_IND_ACC affecting the filling.
It is possible that the engine cannot produce the required engine torque M_IND_ACC. In order to overcome these difficulties, a design is effected in which, during gear shifting, the defaults are sent to the engine control corresponding to the desired defaults of the transmission output torques. However, the friction element is adjusted according to the engine torque which can be realized by the engine. This requires that the engine torque M_IND realizable by the engine be is determined by an engine model which serves, together with the synchronization engine torque M_IND_SYNC, to calculate the transmission output torque during gear shifting, and thereby the friction element control variable to be set.
Overall, a torque coordination is possible with these processes which makes it possible in a stepped automatic transmission, during and outside of gear shifting, to realize continuously running hyperbolic transmission output torques over the vehicle speed, preset, for example, by an accelerator interpreter. Torque discontinuities can thereby be avoided and traction neutrality can essentially be guaranteed.
In gear shifting, it is also possible to differentiate between upshifting and downshifting and correspondingly define suitable embodiments of the invention.
When upshifting, the engine torque M_IND_ACC affecting the filling is preferably set at the beginning of gear shifting to the synchronization engine torque M_IND_SYNC required after gear shifting. A sufficient engine torque potential provided via the filling is thereby available during gear shifting, at least in partial load operation. The adjustment of the engine torque in such a way that a definite speed curve defined by the gear ratio change is followed and preferably remains uninfluenced, except for the slip condition of the friction element of the transmission drive and/or wheel torque, by the correction of the torque M_IND_ACC affecting the filling, is performed by changing the engine torque M_IND_GS affecting the ignition. This engine torque can be calculated by the transmission control and then transmitted to the engine coordinator or directly to the engine control.
When downshifting, the problem arises that while shifting gears, for example, for engine run-up, a larger engine torque must be made available than that necessary in the form of the synchronization torque after shifting gears. If, during downshifting, as in during upshifting, the engine torque M_IND_ACC effective upon filling is set to the required engine torque value after gear shifting M_IND_SYNC, the motor will be unable to build up the necessary action torque in order to move the speed to the synchronization point over the ignition.
As a consequence, the friction element torque must be reduced in order to realize the required engine run-up. A traction-neutral drive trace cannot thereby be attained.
According to a further embodiment of the invention, to prevent this effect, during downshifting the engine torque M_IND_ACC affecting the filling is brought to a sufficient value. For this, a correction torque is calculated which is added to the synchronization torque M_IND_SYNC. In order to provide the correction torque, the torque necessary to increase the speed of the engine is particularly considered. After gear shifting, the engine torque M_IND_ACC affecting the filling is again set equal to the synchronization torque M_IND_SYNC.
Guiding the engine on a default trace in the synchronization point and/or not influencing the transmission output and/or wheel torque by correction of the torque M_IND_ACC affecting the filling, except for the slip condition of the friction element, is performed by setting the dimension M_IND_GS.
Due to physical limits of the engine torque, it is possible, that the engine torque requested by the engine via the above-mentioned engine torques M_IND_ACC and M_IND_GS is not attained. In this case, it is not prudent that (upshifting) and/or possible (downshifting) be used to set the desired output torque at the transmission output. This means that the friction element control and/or adjustment must be dealt with during gear shifting according to corrected defaults, if the engine cannot provide the desired torque. It is important that one knows the torque realizable from the motor. This realignable torque is the torque which can be set via the filling under the current basic conditions. The torque actually realizable from the engine can be calculated from an engine model.
If, according to an embodiment, the torque actually realizable by the engine is smaller than the synchronization engine torque, then a resulting synchronization transmission output torque will be calculated from the synchronization engine torque and a transfer function will be generated based on the transmission output torque before gear shifting, which represents the corrected default for the friction element control or adjustment, respectively, during gear shifting (corrected desired output torque trace).
According to a further embodiment of the invention, the actual filling engine torque M_IND_MOT is calculated from the actually realizable engine torque M_IND and the behavior, over time, of the engine.
A comparison with an engine torque M_IND_AKT, which represents the required engine torque based on the current speed multiplication of the transmission, even during gear ratio changes, provides a reserve engine torque M_IND_RES. This reserve engine torque indicates the engine potential available for realization of the speed defaults during gear shifting. It serves on the one hand for calculation of a dimension M_IND_GSZF, which in turn essentially determines the engine torque M_IND_GS affecting the ignition. The dimension M_IND_GSZF can be transmitted to the engine torque coordinator or directly to the engine control.
On the other hand, the reserve engine torque serves in the determination of whether to intervene in the friction element control and/or adjustment. At an engine potential which is not sufficient to maintain the default speed trace at the default gear shifting conditions, the friction element of the stepped automatic transmission is adjusted in such a way that there is deviation from the corrected desired output torque trace and the required speed trace thus results.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.